Cushings Disease in dogs is not a condition that improves on its own without treatment. The most common cause is a microscopic, benign pituitary tumor, which oversecretes a hormone that causes the adrenals to produce cortisol. Alternatively the adrenals can have a primary tumor that secretes too much cortisol. Half of these tumors are benign and the other half malignant that tend to spread to the lungs and liver.

The result of either of these two tumors is a chronic excess of blood cortisol. In effect, the dog is poisoned with too much cortisol and cannot rely on its own feedback mechanism to regulate the blood cortisol level.